The present invention relates to fuel cells and gas diffusion electrodes which can be used in a variety of applications. The present invention further relates to methods of preparing the fuel cells and other products. The present invention further relates to materials particularly suitable in the manufacture of fuel cells and gas diffusion electrodes and other electrodes.
A gas diffusion electrode (GDE) typically contains a hydrophobic polymer in contact with a high surface area electrically conductive or semiconductive material which supports the finely dispersed catalyst particles. The hydrophobic polymer is usually PTFE (polytetrafluoroethylene), the support material is usually carbon, and the catalyst is usually a metal, such as platinum. The polymer-catalyst-support layer is held by a carbon cloth or a carbon paper. The side of the electrode which contains the catalyst layer is referred to as the “catalytic” side and the opposite side is referred to as the “gas” or gas-permeable side.
A GDE is used in electrochemical processes for bringing gaseous reactants to the reaction sites in contact with an electrolyte. Such an electrochemical process is typically used in a fuel cell for generating electricity. A GDE can be used in an alkaline, phosphoric acid, and proton exchange membrane (PEM) electrolyte fuel cell, also referred to as a solid polymer electrolyte fuel cell (SPFC). The former two electrolytes—alkaline and phosphoric acid—being liquid, can easily bathe the catalyst (or reaction sites) and make good contact with the catalyst for optimum fuel cell performance. A three dimensional reaction zone on an electrode in contact with the electrolyte is not created easily since the PEM electrolyte is a solid. The result is that the efficiency of utilization of the catalyst in a fuel cell reaction involving a PEM electrolyte is low, about 10-20%. Attempts have been made to address this problem by (a) impregnating a small amount of electrolyte solution into the electrode structure, drying the electrolyte and finally pressing the impregnated electrodes against the PEM electrolyte, (b) using a relatively greater proportion of platinum in the platinum/carbon mixture that constitutes the porous electrode, (c) sputtering a thin layer of platinum on top of the porous electrode and, in some limited cases, (d) depositing a layer of platinum on top of the already catalyzed electrode.
Accordingly, fuel cells and gas diffusion electrodes overcoming one or more of the above-described disadvantages are desirable. In addition, fuel cells and gas diffusion electrodes which are less expensive to manufacture and/or operate more efficiently would be preferred in the industry.